Technical Field
The present invention relates to an insulated power supply apparatus applied to a power converter circuit including a series connection of an upper arm switching element and a lower arm switching element. The apparatus includes an upper arm transformer, which can supply drive voltage from a DC power supply to the upper arm switching element, and a lower arm transformer, which can supply drive voltage from the DC power supply to the lower arm switching element.
Related Art
As disclosed in JP-A-11-178356, an insulated power supply apparatus is known which supplies drive voltage to a switching element (IGBT). Specifically, the power supply apparatus includes a plurality of transformers, a transistor, and a control circuit. The transistor is operated so that electricity is conducted between a DC power supply and primary side coils configuring respective transformers or is intercepted therebetween. The control circuit detects output voltage of a secondary side coil configuring one of the plurality of transformers via an electric path connecting between the output side of the secondary side coil and the control circuit. The control circuit operates the transistor based on the output voltage detected via the electric path.
The plurality of transformers configuring the insulated power supply apparatus, the control circuit, which is an integrated circuit, and the like are mounted on a substrate. Depending on the position of one of the transformers, whose output voltage of the secondary side coil is to be detected, on the substrate, the electric path may be lengthened. In this case, the amount of voltage drop in the electric path may be increased, and noise may be superimposed on a voltage signal transmitted over the electric path. In addition, accuracy in controlling the output voltage of the secondary side coil by the control circuit may be lowered, and the control circuit might malfunction.
Note that, to complement accuracy in controlling the output voltage, it can be considered, for example, that a power circuit (e.g. chopper-type step-up circuit) can be provided between the DC power supply and the primary side coils to increase the accuracy in controlling the voltage applied from the DC power supply to the primary side coils. Note that, when operating the step-up circuit, the step-up circuit produces heat. Hence, a concern rises that the heat may adversely affect electronic components mounted on the substrate.